Spin-stabilized projectiles

ABSTRACT

A projectile assembly includes a spin-stabilized projectile having a sub-calibre portion and a discardable sabot mounted on the sub-calibre portion. The sabot is connected to the projectile in such a manner as to prevent separation of the sabot from the projectile, while the rear end of the projectile assembly remains in the barrel of a gun bore from which the projectile assembly is fired, by reason of the axial force exerted on the projectile assembly by the firing gas pressure. The connection allows separation of the sabot from the projectile by the action of centrifugal force and air drag, after the rear end of the projectile assembly has left the muzzle of the gun barrel, by reason of the consequent rapid decrease of the axial force.

United States Patent 1 Friend 1 Nov. 6, 1973 SPIN-STABILIZED PROJECTILES 22 Filed: Oct.23, 1970 [2]] Appl. No.: 83,584

[76] Inventor:

4/1960 France 102/93 815,222 8/1937 France 102/93 Primary Examiner-Robert F. Stahl Attorney-Stevens, Davis, Miller & Mosher 57 ABSTRACT A projectile assembly includes a spin-stabilized projectile having a sub-calibre portion and a discardable sabot mounted on the sub-calibre portion. The sabot is connected to the projectile in such a manner as to prevent separation of the sabot from the projectile, while the rear end of the projectile assembly remains in the barrel ofa gun bore from which the projectile assembly is fired, by reason of the axial force exerted on the projectile assembly by the firing gas pressure. The connection allows separation of the sabot from the projectile by the action of centrifugal force and air drag, after the rear end of the projectile assembly has left the muzzle of the gun barrel, by reason of the consequent rapid decrease of the axial force.

8 Claims, 8 Drawing Figures SPIN-STABILIZED PROJECTILES This invention relates to spin-stabilized projectiles which have a discardable sabot surrounding a subcalibre portion of the projectile.

US. Pat. application Ser. No. 19,057 filed Mar. 12, 1970 in the names of G. V. Bull and L; M. Palacio discloses a projectile which is sub-calibre over the whole of its length and has forward and rear discardable sabots. U.S. Pat. application Ser. No. 62,600 filed Aug. 10, 1970 in the name of W. H. Friend discloses a projectile with a full-bore rear portion and a sub-calibre forward portion carrying a discardable sabot (sometimes referred to as a bourrelet).

A discardable sabot separates from the projectile after it leaves the muzzle of the gun barrel from which it is fired, by the action of centrifugal force and air drag. With some guns, it is desirable to secure an attachment such as a muzzle brake or a flash suppressor to the muzzle end of the barrel. A muzzle brake is used to reduce recoil loads on the barrel support. In this case, it is necessary to ensure that the sabot does not foul the attachment as the sabot is discarded.

According to the present invention, a sabot is prevented from commencing its discarding operation until a predetermined time after the rear end of the projectile has left the muzzle of the gun barrel. During firing, the gas pressure acting on the base of the projectile while it is in the gun barrel is at a high value. As the projectile travels up the barrel, the rifling in the barrel imparts spin to the sabot and projectile. While the sabot is in the barrel, the wall of the barrel bore retains the sabot in assembly with the projectile. Previously, as soon as the sabot leaves the muzzle of the gun, that is to say becomes free from the wall of the gun bore, the centrifugal force acting on the sabot due to its spin causes it to separate from the projectile. In accordance with the present invention, the sabot interlocks with the projectile in such a manner that the gas pressure acting on the projectile while it is in the gun barrel prevents the centrifugal force acting on the sabot from separating the sabot from the projectile. When the rear end of the projectile leaves the muzzle of the gun barrel, the gas pressure acting on the projectile decays and subsequently falls to zero at a distance beyond the attachment. When the gun pressure has decayed to a predetermined lower value, the centrifugal force acting on the sabot is able to separate it from the projectiles, and air drag assists with the separation. It is therefore arranged that the sabot does not commence to separate from the projectile until some time after the rear end of the projectile has left the muzzle of the gun barrel,

so that separation of the sabot from the projectile does not occur until the sabot is clear of the attachment.

The required interlocking of the sabot and projectile may be provided by an undercut recess in the projectile with a correspondingly shape lug on the sabot fitting therein. The undercut recess may be directed forwardly or rearwardly according to whether the axial force acting on the sabot relative to the projectile is forwardly or rearwardly. Where the sabot is located on a forward portion of the projectile, the wall of the barrel will cause a rearward force to be applied to the sabot relative to the projectile, and the undercut recess will therefore extend rearwardly. On the other hand, when the sabot is adjacent the rear end of the projectile, such that the gas pressure acts on the sabot, the sabot will be subject to an axial force forwardly relative to the projectile, and the undercut recess will extend forwardly.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, of which:

FIG. 1 is a sectional side view ofa projectile assembly according to one embodiment,

FIG. 2 is a similar view of the main body of the pro jectile,

FIG. 3 is an enlarged sectionalview of. the portion of the main body indicated at A in FIG. 2,

FIG. 4 is an enlarged sectional view of a portion of the main body indicated at B in FIG. 2,

FIG. 5 is a sectional view taken along the line 5-5 of FIG. 1,

FIG. 6 is a sectional view taken along the line 6-6 of FIG. 1,

FIG. 7 is a sectional view of a projectile assembly according to a second embodiment, and

FIG. 8 is a sectional side view of a projectile assembly according to a third embodiment.

Referring to the accompanying drawings, a projectile assembly includes a sub-calibre projectile l with a main body 2, a nose portion 3 screwed into a threaded bore 4 in the main body 2, and a rear portion 5 screwed into a threaded bore 6 in the main body 2. The projectile l carries a rear sabot 7 adjacent its rear end, and a for ward sabot 8 at a position approximately half-way along the length of the projectile and forwardly of its centre of gravity. The projectile tapers from the rear sabot 7 to the forward end of the nose portion 3.

The rear sabot 7 includes three equal arcuate segments 9 held in place by a driving band 10 encircling the segments 9. The driving band 10 is located in an annular groove in the segments 9, and has an annular projection 11 which engages rifling in the gun barrel, from which the projectile is tired, so that spin is imparted to the sabot 7 and to the projectile during firing. The driving band 10 has a series of annular grooves 12 to receive metal of the driving band which is displaced when the projectile is in a barrel. The mutually-engaging surfaces of the segments 9 and the driving band 10 are irregular to assist in transfer of thrust and spin from the driving band 10 to the segments 9. A second driving band 10a is located in an annular groove at the forward end of the segments.

The mutually-engaging surfaces of the segments 9 and the projectile body 2 are stepped at 13 to assist the transfer of thrust from the sabot 7 to the projectile. Also, to assist the transfer of spin from the sabot 7 to the projectile, each segment 9 is keyed to the projectile body 2 by a longitudinally-entending key 14 located in a recess formed partly in the segment 9 and partly in the body 2.

To prevent the rear sabot 7 from becoming detached from the projectile until after the projectile has left the muzzle of the gun barrel, the segments 9 are locked to the projectile in a radial sense at their forward and rear ends. The forward end of each segment has a forwardly extending lug IS located in an annular forwardly extending undercut-recess in the projectile body 2. The rear end of each segment 9 has a forwardly extending lug 16 located in an annular forwardly extending undercut-recess in the rear portion 5. An obturator 17 forms the rear end of the projectile assembly and is held in place by snapping engagement with the rear end portion of the segments 9.

The forward sabot 8 has three equal arcuate segments 18 each with an inwardly directed nose 19 located in an annular recess 20 in the projectile body 2. Each nose 19 has a rearwardly directed lug 21 located in an undercut rearward extension 22 of the recess 20.

The length of the recess 20 is sufficiently long to enable the lug 21 to move out of the rearward undercut extension 22 of the recess 20. The segments 18 are retained in position by an annular driving band 23 encircling the segments 18 and located in a recess therein.

When the projectile assembly is fired, the forward driving band 23 centres the leading end of the projectile in the gun bore, and the rear driving band imparts spin to the projectile. The forward thrust exerted by the gases on the projectile assembly causes the lugs 21 to be retained in the respective recesses in the main body 2 and rear portion 5.

When the forward sabot 8 leaves the barrel, the sabot 8 is retained in place on the projectile because of the retention of the lugs 21 in the recess extension 22 by the axial forward thrust, which provides a resistance to disintegration of the sabot by the centrifugal force caused by the projectile spin. After the rear end of the projectile has left the muzzle of the barrel, the axial forward thrust quickly decreases to a value such that, the centrifugal forces cause disintegration of the driving band 23, with the result that the lugs 21 are no longer retained in the recess extension 22. The segments 18 then leave the projectile body 2 under the influence of centrifugal force and air drag, with the lugs 21 sliding readily out of the recess extension 22 owing to the adequate length of the recess 20.

Similarly, the rear sabot 7 is prevented from commencing disintegration until after the rear end of the projectile assembly has left the muzzle of the barrel. When the forward axial thrust has decreased by a sufficient amount, the centrifugal force having caused disintegration of the driving bands 10 and 10a the lugs and 16 are no longer forcibly retained in their respective undercut recesses, and the segments 13 leave the projectile under the influence of centrifugal force and air drag. The obturator 17 is also separated by air drag.

In this manner, the separation of each sabot from the projectile is delayed sufficiently until it has cleared the muzzle brake. The specific design of the interlocking parts of the sabots and the projectile is based on the muzzle brake design, the projectile spin rate, projectile velocity at muzzle, and the rate of pressure decay beyond the muzzle adjacent the muzzle brake.

Although the sub-calibre projectile described above has relatively widely separated forward and rear sabots,

- it is possible to replace the two sabots by a single sabot which extends forwardly and rearwardly of the centre of gravity of the projectile.

FIG. 7 shows a second embodiment in which the projectile has a full calibre rear portion and a sub-calibre forward portion. The projectile assembly includes a projectile 31 having a main body 32, a nose portion 33 screwed into a threaded bore 34 in the forward end of the main body 32, and a rear portion 35 screwed into a threaded bore 34 in the rear end of the main body 32.

Adjacent its rear end, the main body 32 has an annular groove in which a driving band 40 is located. The driving band 40 has an annular projection 41 which engages the rifling in the barrel, and a series of annular grooves 42 to receive metal of the driving band. Behind the driving band 40, the main body 32 has a short section of substantially full calibre, and rearwardly of the section the body tapers toward its rear end. The diameter of the main body 32 immediately in front of the driving band is substantially full calibre, and tapers continuously throughout the main body 32 and nose portion 33 to the forward end of the nose portion 33.

On its tapering portion, the main body 32 carries a sabot 38 including 3 arcuate segments 48 each with an inwardly directed nose 49 and rearwardly extending lug 51 located in a recess with a rearward undercut extension in the main body 32, the segments 48 being held in place by an annular driving band 53. The sabot 38 and its attachment to the projectile body is identical to the forward sabot 8 and its connection to the main body of the previously described projectile assembly illustrated in FIGS. 1 to 6.

Upon firing, the sabot 38 separates from the projectile after the rear end of the projectile has left the muzzle of the gun barrel, in the same manner as described in the previous embodiment. The driving band 40 mounted on the full bore rear portion of the projectile remains in assembly with the projectile body during firing and flight.

FIG. 8 shows a third embodiment similar to the embodiment shown in FIGS. 1 to 6. The projectile assembly includes a sub-calibre projectile 61 having a main body 62, a nose portion 63, and a rear portion 65. The projectile 61 is fitted with a rear sabot 67 and a forward sabot 68.

The rear sabot 67 includes segments 69 held in place by driving bands 60 and 60a. The mutually engaging surfaces of the segments 69 and projectile l are knurled at 73 to assist the transfer of spin from the sabot 67 to the projectile 61. The knurled mutually engaging surfaces taper rearwardly and the leading ends of the segments 69 are shaped as noses 75 which engage in an annular recess in the projectile 61. The rear portions of the segments 69 have forwardly-directed noses 76 which engage in an annular groove in the projectile 61. The rear mutually-engaging surfaces of the segments 69 and projectile 61 taper forwardly at 76a, as shown. An obturator 77 is snapped onto the segments 69.

The 'forward sabot 68 is similar to the sabot 8 described with reference to FIGS. 1-6 except that the mutually-engaging surfaces of the noses 79 and lugs 80 of its segments 78 and the projectile taper rearwardly from the outer surface of the projectile.

The projectile assembly shown in FIG. 8 functions in a similar manner to the previously described embodiments. The forward taper 76a prevents forward move ment of the projectile relative to the rear sabot 67 before disengagement of the sabot 67.

Another advantage of all the embodiemnts is that, if the projectile assembly is fired from a worn gun, partial separation of the sabots from the projectile of centrifugal force, when the assembly is in a gun barrel, is prevented by the interlocking of the sabots and projectile according to the invention.

Iclaim:

l. A projectile assembly having a releasable sabot comprising:

a. a projectile assembly including a spin-stabilized projectile having a sub-caliber portion;

b. a discardable sabot mounted on the sub-caliber portion;

0. means for delaying release of the sabot for a predetermined time after the projectile assembly has left the mouth of a gun barrel comprising:

l. a circumferentially extending groove on the projectile having an under-cut recess;

2. said sabot having a series of arcuate segments with each segment having an inwardly directed nose which extends into said groove;

3. each said nose having a longitudinally extending lug which engages in said under-cut recess to prevent separation of the sabot from the projectile assembly until after the entire assembly has left the barrel.

2. A projectile assembly according to claim 1 wherein said lug extends rearwardly from the nose.

3. A projectile assembly according to claim 2 wherein the segments and the projectile have rearwardly tapering surfaces.

4. A projectile assembly according to claim 4 wherein said lug extends forwardly from a forward end of the segment.

5. A projectile assembly according to claim 4 wherein the lug extends forwardly from a rear end of the segment.

6. A projectile assembly according to claim 1 wherein the projectile carries a forward sabot and a rear sabot, each sabot including a series of arcuate seg ments, each of which have a lug engaged in an undercut recess in the projectile.

7. A projectile assembly according to claim 1 wherein the projectile has a full-calibre rear portion and a sub-calibre forward portion, said sabot being mounted on said forward portion.

8. A projectile assembly according to claim 1 wherein the lug extends forwardly from the segment, and said segments and the projectile have forwardly tapering mutually-engaging surfaces to prevent forward movement of the projectile relative to the sabot before disengagement of the sabot. 

1. A projectile assembly having a releasable sabot comprising: a. a projectile assembly including a spin-stabilized projectile having a sub-caliber portion; b. a discardable sabot mounted on the sub-caliber portion; c. means for delaying release of the sabot for a predetermined time after the projectile assembly has left the mouth of a gun barrel comprising:
 1. a circumferentially extending groove on the projectile having an under-cut recess;
 2. said sabot having a series of arcuate segments with each segment having an inwardly directed nose which extends into said groove;
 3. each said nose having a longitudinally extending lug which engages in said under-cut recess to prevent separation of the sabot from the projectile assembly until after the entire assembly has left the barrel.
 2. A projectile assembly according to claim 1 wherein said lug extends rearwardly from the nose.
 2. said sabot having a series of arcuate segments with each segment having an inwardly directed nose which extends into said groove;
 3. each said nose having a longitudinally extending lug which engages in said under-cut recess to prevent separation of the sabot from the projectile assembly until after the entire assembly has left the barrel.
 3. A projectile assembly according to claim 2 wherein the segments and the projectile have rearwardly tapering surfaces.
 4. A projectile assembly according to claim 4 wherein said lug extends forwardly from a forward end of the segment.
 5. A projectile assembly accoRding to claim 4 wherein the lug extends forwardly from a rear end of the segment.
 6. A projectile assembly according to claim 1 wherein the projectile carries a forward sabot and a rear sabot, each sabot including a series of arcuate segments, each of which have a lug engaged in an undercut recess in the projectile.
 7. A projectile assembly according to claim 1 wherein the projectile has a full-calibre rear portion and a sub-calibre forward portion, said sabot being mounted on said forward portion.
 8. A projectile assembly according to claim 1 wherein the lug extends forwardly from the segment, and said segments and the projectile have forwardly tapering mutually-engaging surfaces to prevent forward movement of the projectile relative to the sabot before disengagement of the sabot. 